The term wheelmotor, as used hereinafter, applies to a hydraulic motor with a rotating case and a stationary shaft. A hydraulic motor is a multicylinder radial piston engine driven by recirculating hydraulic fluid under high pressure. Wheelmotors are used, for example, to drive conveyor belts, bulldozers, excavators, other construction equipment and, by the airlines, to drive the tow trucks that maneuver aircraft in their hangars. The wheelmotor accordingly is not a new device but, to my knowledge, it has not previously been used "wet" in underwater service, notably, to drive the cutter head of a dredge.
The more familiar rotating shaft hydraulic motor, on the other hand, has been used exclusively to drive the bucketwheels of dredges of the prior art. These latter motors may be mounted on deck, above water, remote from the bucketwheel to which they connect by a power train of shaft- or chain- drive interlinked by gear box or their sprocket equivalents. These motors are also used for "dry" underwater service, in which case they are housed in a watertight dry chamber where they are spaced from the bucketwheel hub itself by an intervening gearbox filled with oil under pressure to avoid the intrusion of water, as is recited by John A. Neumann in U.S. Pat. No. 4,395,833, dated Aug. 2, 1983.
Now I have discovered that the VALMET.TM. wheelmotor, manufactured by Valmet Hydraulics, Sulantie 19, SF-04300 HYRYLA, Finland, and sold in the U.S.A. under the brand name Black Bruin.TM. by the distributor, North American Hydraulics, Inc., P.O. Box 40062, Houston, Tex., 77240, is eminently suited for wet operation under water in contrast to the above described dry underwater operation with rotating shaft motors in the prior art.
Although my experience with the Black Bruin.TM. and other wheelmotors in wet underwater service, absent optional added protection from water intrusion, has been favorable so far, I am mindful, nevertheless, of the history of eventual failure of rotating shaft hydraulic motors due to corrosion and excessive wear induced by water and abrasive mud ingested into the motor bearings under these conditions. It is believed that the bearing seal in the wheelmotor is superior to that in the rotating shaft motor, but in any event, the bearing seal is the last line of defense against water intrusion. Accordingly, in a preferred embodiment of the invention I provide first and second lines of defense against water intrusion consisting respectively, of:
1. a compression seal, essentially a thick-walled cylinder, adapted to be lodged in longitudinal compression against the peripheral annular portion of the inboard flat, circular, hub surface of the back plate surrounding the stationary shaft part of the wheelmotor with its first end in sliding engagement therewith and, with its second end to encircle and firmly grasp the substantial conical surface area of the rotating case of the wheelmotor wedged in the second end, whereby the seal rotates in locked engagement with the case and encloses a watertight compartment around the junction of the stationary shaft and the rotating case. And
2. a threaded hole in the wall of the compression seal adapted to interchangeably and alternately receive a grease compression fitting or an Allen head plug, whereby all of the air enclosed within the compartment can be expelled with pressurized grease from a grease gun, and thereafter the grease fitting is replaced by the plug.
The Black Bruin.TM. wheelmotor is fortuitously provided with a prominent and substantial conical surface area which converges toward the stationary shaft end of the motor. This simplifies the practice of the preferred embodiment of the invention. A competitive wheelmotor offered by Rotary Power also provides the desired conical surface. Although it is relatively stubbier and larger in diameter, a compression seal can be adapted to accommodate it by changing the dimensions as well as by adopting a new more suitable surface of revolution shape, such as the frustum of a cone, a horn or a sphere, etc.